The invention will have applications, for example, in motor vehicles for informing and/or guiding the users of the vehicle, in particular its driver.
It is known to equip a motor vehicle with head-up display equipment, also known as a head-up display or HUD (standing for “Head-Up Display” in English). Such a display is placed in the field of vision of the motor vehicle's driver and displays information relative to the state of the vehicle, the traffic or other things.
This type of head up display device for a motor vehicle makes it possible to obtain an image with sufficient brightness for the user, and notably the driver of the vehicle, to be able to see the image sufficiently, and in any situation, day or night and according to the meteorological conditions (sunny or cloudy).
Among the possible technologies for forming such an image by means of the head-up display device, the one most used in the prior art is the liquid crystal display technology, notably the TFT-LCD (standing for “Thin-Film Transistor Liquid Crystal Display” in English) technology. These TFT-LCD display screens necessitate, for the display of an image, backlighting generally carried out by a plurality of light emitting diodes or LEDs (LED standing for “Light-Emitting Diode” in English). In practice, this TFT-LCD screen and the backlighting are comprised in an assembly called an image generating device and also known by the English word “imager”.
Downstream of the screen in the direction of movement of the light beams, the head-up display device generally comprises a semi-reflecting lamina, called a “combiner” in English, or a semi-reflecting area of windscreen and, between the screen and the combiner or windscreen, a reflection device with one or more flat or concave mirrors.
This image is displayed through the semi-reflective lamina and with magnification by reflection and seems to appear beyond, and therefore in front of the windscreen of the vehicle.
However, as a function of the users, it is necessary to be able to adjust the position, notably the height, of the image projected on the windscreen in order to take account for example of the height of the driver.
At present, head-up display devices are known where a motor is engaged directly or via pinions or endless screws, with a pivoting axis of the last deflecting mirror, which makes it possible to adjust the height of the image on the windscreen.
However, the system is very sensitive such that it is necessary to use stepper motors with very fine angular resolution which are very costly. Moreover, the known systems are subject to vibration problems when the vehicle is moving. If the projected image also vibrates it would then be difficult to read or would even be illegible.